The easy to access and produce hydrocarbon resources are being depleted leaving more difficult wells to access and produce. Meeting the world's growing demand for hydrocarbons resulted in the development of advanced recovery procedures, often referred to as complex recovery completions and production techniques. These methods may include Steam Assisted Gravity Drainage (SAGD), Thermal Assisted Gravity Drainage (TAGD), Toe to Heal Air Injection (THAI), Vaporized Hydrocarbon Solvent (VAPEX) production and Fire Flooding. These techniques address the mobility problem of the heavy oil wells by thermally and/or chemically altering the viscosity of the bitumen to allow for easy extraction. While each of the complex completion techniques offers a novel approach to heavy oil extraction, their success may rely on the difficult process of precise placement of wellbores with respect to near-by geological structures.
One difficult scenario includes local deposits that have the potential to cause steam to break through, resulting in a non-optimal steam chamber. In this case, as steam is injected from the injector well, it breaks through above or below the deposits and results in insufficient heating of bitumen and, thus, reduction in production.
In one solution, producer wells are placed using resistivity or gamma logs to detect formation layering from a distance. In this case, a distance to nearby layering is used to optimally place the producer well in the reservoir by geosteering the drilling. After the producer well is placed, the injector well is placed with respect to the producer well using ranging devices that can measure the relative distance and direction between the two wells.
Well-known commercial approaches for this technique are based on rotating magnets (e.g., U.S. Pat. No. 5,589,775) or magnetic guidance (U.S. Pat. No. 5,923,170) that utilize both wellbores for ranging. Most of these approaches, however, are undesirable in that they use two different crews (i.e., wireline and logging while drilling (LWD)), which is not cost effective. One prior magnetic approach is based on a single well system where both the transmitter and the receivers are downhole. This approach, however, is based on absolute magnetic field measurement for distance calculation (U.S. Pat. No. 7,812,610) that does not produce reliable results due to variations of the current on the target pipe.
Additionally, the prior art techniques typically place the injector well a fixed distance above the producer well. The selection of the fixed distance may be made heuristically without considering geological and petrophysical variations. This may result in placement of the injector well at non-optimal positions and reduction in volume of accessible hydrocarbons.